The present invention relates to a radiant infra-red heated spray paint booth, the purpose of which is to more efficiently dry the objects being painted. The booth is particularly well suited for painting automotive vehicles but it will be understood, and will become apparent as the description proceeds, that virtually any object can be painted and dried in the booth.
Ever since the introduction of mass production techniques in respect to the rapid drying of freshly painted surfaces, the painting industry, on both large and small scale, has constantly sought ways to improve the rate and quality of paint drying operations. Large manufacturers frequently can justify the space requirements and consequent cost necessary for separate painting and paint drying areas. In those situations where the paint drying is performed to the exclusion of painting, the use of direct radiant heat accompanied by either heated forced air or natural convection has been employed. Under these circumstances, the operators of the drying apparatus can carefully control the flow of heated air around and over the paint surface to be dried. The cost of providing equipment to furnish both heated air as well as direct radiant heat bear negatively upon the economy of this approach. At the present time with energy costs escalating the use of both direct radiant heat and forced convection heat becomes economically undesirable.
It is well known that the rate of heat transfer is much greater for radiation heating than for any other type of heating, because the heat transfer by radiation is direct, immediate and constant throughout the process. With convection or conduction heating, the heat capacity of the medium enters is often a detrimental factor. The thermal capacity of air is relatively small, and it therefore takes considerable time to transfer a large amount of heat from the source to the air and from the air to the workpiece. It is obvious therefore that direct heat transfer is a more economical method of heat transfer than by convection.
One example of the combined methods of connective and conductive heat transfer is shown in U.S. Pat. No. 3,151,950 which discloses direct radiant heating while simultaneously introducing forced convection heating to a painted surface to be dried. This patented system represents a most complex and costly approach to drying paint.
Direct heat transfer by radiation is frequently accomplished by a bank of infra-red filament lamp sources. Most of these banks of infra-red lamps contain dozens if not hundreds of individual lamps due to the fact that the lamp filament, which emits electromagnetic energy in the wave length of infra-red, is very small. The rate of emission is an important factor in determining the rate of absorption in a paint absorbing medium, i.e. the rate of heating depends on the rate of emission. The higher the temperature, the higher are the relative peak intensitites of the respective radiating surfaces where the two emitters are of the same surface area. Each lamp in the bank has a small filament and therefore a small emitter surface. Accordingly, a multitude of lamps in close proximity are required to provide an evenly distributed application of heat to the painted surface to be dried. The maintenance costs and lamp replacement efforts required of these arrangements detract from their economy and usefulness. Additionally, the lamp breakage is a safety hazard, not to mention hot spots that are created by the physical appliances that hold the lamps.
U.S. Pat. No. 2,498,339 illustrates the use of multiple heating lamps in an upper chamber of a two chamber combination spray paint and baking oven. The oven employs heat lamps to dry or bake the freshly painted auto finish, and the auto is first painted in the lower chamber and thereafter lifted into the baking oven.
The desirability of employing energy sources other than electricity to cause the emission of infra-red energy have led others to provide a radiant burner with the combustion products of air and gas. Referring to U.S. Pat. No. 3,299,938, the combustion products pass through a porous structure that in turn becomes an emitter of infra-red energy. The gas fired radiant heater introduces the combustion product directly into the zone to be heated along with the infra-red energy. Introduction of such high temperature combustion products into a paint filled atmosphere could result in an explosive situation.
In view of the above noted disadvantages in the art, efforts were previously made by applicant to provide a satisfactory and efficient solution to the problem of paint drying in booths of the type described. These efforts, however, were not entirely successful since glass panels, forming part of a radiant heater assembly, could not be obtained which would not shatter after relatively short periods of use. The temperature in the vicinity of the radiant pipe is approximately 900.degree. F. and glass panels used prior to the present invention simply do not withstand such temperatures and shatter after a relatively short period of time.